Blind fasteners are commonly used to secure workpieces together when it is otherwise impossible to access the blind side of one of the workpieces. Typically, the workpiece that is accessible by an end-user is referred to as the accessible side workpiece and the workpiece that is inaccessible by an end-user is referred to as the blind side workpiece.
Blind fasteners have wide application in the aerospace industry. In aerospace applications, the blind fastener assembly of the present invention can be used to secure workpieces made of aluminum alloy, other metallic alloys, composites or combinations thereof.
An example of a previously available blind fastener is disclosed in U.S. Pat. No. 2,971,425. The principle components of the blind fastener of this prior art patent are a screw, a bushing, and a threaded nut. Generally, this prior art screw, bushing and threaded nut are similar in construction in certain aspects to the pin member and sleeve of the present invention. Distinctions between this prior art fastener and the present invention will focus on the embodiment of the prior art fastener that has recesses disposed in the head of the bushing that is adapted receive nibs of a nose that is affixed to a standard installation tool.
To install this prior art fastener, a nose with a plurality of nibs disposed on one side of the exterior surface thereof is provided that is affixed to a standard installation tool. Also, a driver configured to engage the driving head of the screw is provided that is affixed to the standard installation tool. The driver is engaged with the driving head of the screw and the nibs of the nose are disposed within the recesses of the bushing. The recesses in the bushing of this prior art fastener would need to be relatively deep like the recesses used in the commercial embodiments of the fasteners shown and described in U.S. Pat. Nos. 5,498,110 and 5,634,751. The deep recesses are needed in order to promote engagement between the nibs of the nose and the recesses of the bushing. Unfortunately, the use of deep recesses would weaken the bushing. In operation, the driver would rotate the screw and the nibs of the nose would engage the recesses in the head of the bushing in an attempt to prevent rotation of the bushing relative to the screw. Formation of the blind side bulb is supposed to be facilitated by threading the screw into the stationary bushing.
Such an operation would not effectively form the blind side bulb to clamp a plurality of workpieces together because the nibs of the nose would cam-out of the recesses during the installation of this prior art fastener. When the nibs cam-out of the recesses, the bushing rotates relative to the nose thereby causing wear damage to the nibs of the nose due to the abrasion of the nibs rotating against the head of the bushing. As can be appreciated, the nose would need to be frequently replaced due to the wear the nibs would experience in such a system. Additionally, the rotation of the bushing relative to the screw is undesirable from the standpoint of forming the blind side bulb. Optimum installation performance and reliability in bulb formation are not achieved with such an approach.
Rotation of the bushing would also cause abrasion or scraping of the head of the bushing by the nibs rotating against the head of the bushing. These results are not only visually apparent, but can also deteriorate the corrosion resistant properties of the bushing. Factors such as improper bulb formation, inconsistent structural clamp up and shear strength compromise the integrity of this prior art blind fastener.
With this prior art fastener, an end-user of the fastener attempts to prevent cam-out of the nibs from the recesses of the bushing by exerting a pushing force against the installation tool in order to maintain the engagement of the nibs with the recesses of the bushing. As can be appreciated, the end-user would become fatigued with applying such a force against the installation tool.
Of particular distinction to U.S. Pat. No. 2,971,425, the recesses in the head of the sleeve of the present invention slope rearwardly towards the blind side workpiece. These recesses are adapted to be engaged with nibs disposed on one end of a nose of a nose assembly affixed to a standard rotary installation tool. These nibs also slope rearwardly towards the blind side workpiece. Engagement of the sloping nibs with the sloping recesses is particularly advantageous in preventing rotation of the sleeve relative to the pin member during installation of the blind fastener of the present invention. Utilization of sloping nibs and recesses eliminates cam-outs. As such, the problems associated with cam-outs related to the design of U.S. Pat. No. 2,971,425 is eliminated. Additionally, by eliminating the cam-out problem associated with prior art fasteners by using the rearwardly sloping nibs and recesses, the recesses of the present invention are relatively shallow as compared to the deep recesses used in the commercial embodiment of the fasteners shown and described in U.S. Pat. Nos. 5,498,110 and 5,634,751. The shallow recesses of the present invention do not significantly weaken the sleeve of the present invention like the deep recesses used in the prior art.
Additionally, the driving head of the pin member of the present invention has splines or threads disposed on the exterior surface of the driving head. As used herein, the term “splines” means splines or threads. These splines are adapted to be engaged with a splined driver of a nose assembly affixed to a standard rotary installation tool. The splined engagement between the driving head and the driver is particularly advantageous in simultaneously pulling the installation tool towards the fastener during actuation of the tool to ensure proper engagement of the nibs with the recesses and rotatably torquing the pin member to effectively form the blind side bulb of the fastener. The pulling feature of the splined engagement between the pin member and driver to ensure engagement of the nibs with the recesses also eliminates the problems associated with cam-outs related to the design of U.S. Pat. No. 2,971,425.